Nucleocapsid-specific antibodies as a correlate of protection against SARS-CoV-2 reinfection in children
Authors: Alexander C. Dowell, Dagmar Waiblinger, John Wright, Shamez N. Ladhani, Paul Moss
Journal: Journal of Infection (2023)

SARS-CoV-2 infection confers relative protection against reinfection, albeit short-term and incomplete,1Bobrovitz N. Ware H. Ma X. Li Z. Hosseini R. Cao C. et al.Protective effectiveness of previous SARS-CoV-2 infection and hybrid immunity against the omicron variant and severe disease: a systematic review and meta-regression.Lancet Infect Dis. 2023; 23: 556-567Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar and improved immune correlates and vaccine approaches are required to reduce the prevalence of reinfection. Spike-specific antibody titres associate with protection in adults2Yamamoto S. Mizoue T. Ohmagari N. Analysis of previous infection, vaccinations, and anti–SARS-CoV-2 antibody titers and protection against infection with the SARS-CoV-2 Omicron BA.5 variant.JAMA Netw Open. 2023; 6 (e233370-e233370)Crossref Scopus (10) Google Scholar whilst both infection3Mensah A.A. Campbell H. Stowe J. Seghezzo G. Simmons R. Lacy J. et al.Risk of SARS-CoV-2 reinfections in children: a prospective national surveillance study between January, 2020, and July, 2021, in England.Lancet Child Adolesc Health. 2022; 6: 384-392Abstract Full Text Full Text PDF PubMed Scopus (41) Google Scholar and vaccination were protective in children during the initial phases of the pandemic.4Cohen-Stavi C.J. Magen O. Barda N. Yaron S. Peretz A. Netzer D. et al.BNT162b2 vaccine effectiveness against Omicron in children 5 to 11 years of age.N Engl J Med. 2022; 387: 227-236Crossref PubMed Scopus (61) Google Scholar However, the omicron variant shows increased infectivity and protection afforded by ancestral-spike based vaccines has diminished markedly.4Cohen-Stavi C.J. Magen O. Barda N. Yaron S. Peretz A. Netzer D. et al.BNT162b2 vaccine effectiveness against Omicron in children 5 to 11 years of age.N Engl J Med. 2022; 387: 227-236Crossref PubMed Scopus (61) Google Scholar, 5Dimeglio C. Migueres M. Bouzid N. Chapuy-Regaud S. Gernigon C. Da-Silva I. et al.Antibody titers and protection against Omicron (BA.1 and BA.2) SARS-CoV-2 infection.Vaccines. 2022; : 10PubMed Google Scholar Aligned with this, the predictive utility of spike-specific antibody responses is now less clear.5Dimeglio C. Migueres M. Bouzid N. Chapuy-Regaud S. Gernigon C. Da-Silva I. et al.Antibody titers and protection against Omicron (BA.1 and BA.2) SARS-CoV-2 infection.Vaccines. 2022; : 10PubMed Google Scholar Here we studied SARS-CoV-2 reinfection in school children during an 8-month period encompassing the omicron BA.4/5 wave and related this to baseline antibody titres against spike and nucleocapsid. 125 children aged 4–15 years with clinical or serological history of prior SARS-CoV-2 infection were recruited to study (median [IQR] age 11.0 [9–13] years; 53 boys, 71 girls, 1 not provided). Baseline serum samples were collected during Jan-May 2022 with follow-up serum samples taken between Oct-Dec 2022 after a median interval of 8.7 months [8.3–8.7] (Supplementary Fig. 1), further details are provided in Supplementary methods. A 1.5-fold rise in nucleocapsid-specific antibody titre between sampling dates was used to define reinfection. Nucleocapsid-specific antibody titres show considerable waning after infection6Dowell A.C. Butler M.S. Jinks E. Tut G. Lancaster T. Sylla P. et al.Children develop robust and sustained cross-reactive spike-specific immune responses to SARS-CoV-2 infection.Nat Immunol. 2022; 23: 40-49Crossref PubMed Scopus (115) Google Scholar and this increment is therefore a reliable correlate of reinfection. 23 (18%) children had received primary COVID-19 vaccine prior to study, while 27 (22%) received primary vaccine during follow-up. No association was seen between baseline spike-specific-IgG titre and incidence of reinfection. In contrast, baseline nucleocapsid-specific-IgG titres were strongly associated with protection from reinfection, (p < 0.0001, Kruskal-Wallis test with Dunn's multiple comparisons test) (Fig. 1A). Children with nucleocapsid-specific titres below the median value at baseline (14,390 AU/ml; 34 BAU/ml) had a 60% rate of reinfection (37/62) compared to 16% in children above median values (10/63). The odds ratio (OR) for protection was 7.8 (95% CI 3.4–18), p < 0.0001). ROC curve analysis of spike (AUC 0.57 (0.46–0.67) and nucleocapsid-specific titres (AUC 0.83 (0.77–0.90), p < 0.0001) showed the median nucleocapsid-specific-IgG titre to be of significant predicative value (Fig. 1B). In order to determine if the protective association with nucleocapsid-specific titre could reflect the impact of recent infection we assessed 32 children who had a documented omicron infection immediately prior to baseline serology collection and within this group 64% of those below the defined nucleocapsid titre developed a subsequent reinfection (9/14) compared to only 22% (4/18) of those above median titre. As such these data indicate that the protective association with nucleocapsid titre is not solely a result of recent infection (p = 0.0077, two-tailed Mann-Whitney test; OR 8.1 (95% CI 1.7–37.8) (Supplementary Fig. 2). The mechanism by which nucleocapsid-specific antibody titre may protect against reinfection is unclear. SARS-CoV-2 nucleocapsid phosphoprotein links the viral genome to the viral membrane and is relatively conserved between coronaviruses. Nucleocapsid-specific antibodies are generated reliably after SARS-CoV-2 infection and although titres have not previously been defined as a correlate of protection recent studies demonstrate an important role in immune defence. Combined vaccination with spike and nucleocapsid enhances protection against omicron infection in animal models although nucleocapsid vaccination alone was not assessed.7Hajnik R.L. Plante J.A. Liang Y. Alameh M.G. Tang J. Bonam S.R. et al.Dual spike and nucleocapsid mRNA vaccination confer protection against SARS-CoV-2 Omicron and Delta variants in preclinical models.Sci Transl Med. 2022; 14: eabq1945Crossref PubMed Scopus (47) Google Scholar Furthermore, nucleocapsid-specific monoclonal antibodies can improve clinical control of SARS-CoV-2 in infection models.8Dangi T. Sanchez S. Class J. Richner M. Visvabharathy L. Chung Y.R. et al.Improved control of SARS-CoV-2 by treatment with a nucleocapsid-specific monoclonal antibody.J Clin Investig. 2022; 132: 23Crossref Scopus (25) Google Scholar Although we see a strong association between the titre of nucleocapsid-specific antibodies and risk of reinfection there was no such relationship with spike-specific responses, the latter observation is somewhat surprising given the proven utility of spike-containing vaccines to reduce infection rates. However, it is important to note that our study addressed risk of reinfection rather than risk of primary infection. As such, relative titres of antibody against spike and nucleocapsid may play a differential protective role following initial infection. Spike-targeted vaccines are much less effective at protection against reinfection in the era of omicron variants1Bobrovitz N. Ware H. Ma X. Li Z. Hosseini R. Cao C. et al.Protective effectiveness of previous SARS-CoV-2 infection and hybrid immunity against the omicron variant and severe disease: a systematic review and meta-regression.Lancet Infect Dis. 2023; 23: 556-567Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar, 9Lin D.-Y. Gu Y. Xu Y. Zeng D. Wheeler B. Young H. et al.Effects of vaccination and previous infection on omicron infections in children.N Engl J Med. 2022; 387: 1141-1143Crossref PubMed Scopus (30) Google Scholar and it is possible that nucleocapsid-specific antibodies, which elicit strong antibody directed cell cytotoxicity, play a more important role in preventing reinfection. The strong conservation of nucleocapsid sequence between SARS-CoV-2 variants compared to spike may contribute to this effect. The potential duration of protection afforded by a robust nucleocapsid-specific antibody response is uncertain, but we observed that antibody titres decreased with a half-life of 3.0 months within children who remained uninfected and took an average of 7.4 months to fall to the median value (Fig. 1C). Nucleocapsid-specific antibodies may cross react against seasonal coronaviruses (HCoV) and OC43 nucleocapsid-specific responses have been associated with relative protection against primary SARS-CoV-2 infection.10Lavell A.H.A. Sikkens J.J. Edridge A.W.D. van der Straten K. Sechan F. Oomen M. et al.Recent infection with HCoV-OC43 may be associated with protection against SARS-CoV-2 infection.iScience. 2022; 25105105Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar However, HCoV-specific responses are themselves of short duration and unlikely to fully explain our observations.11Edridge A.W.D. Kaczorowska J. Hoste A.C.R. Bakker M. Klein M. Loens K. et al.Seasonal coronavirus protective immunity is short-lasting.Nat Med. 2020; 26: 1691-1693Crossref PubMed Scopus (483) Google Scholar Of note, this study cannot define the nucleocapsid-specific response as the causal determinant of protection as antibody titre may represent an indirect measurement of the quality of the immune response generated after initial infection. However, it is noteworthy that such an association is not seen with the spike-specific response. In conclusion, we show that levels of nucleocapsid-specific antibodies correlate with protection against SARS-CoV-2 reinfection in children. This reveals the need for improving our understanding of correlates of protection and indicates that vaccines containing nucleocapsid protein should be prioritised for clinical assessment. The authors declare no competing interests. sKIDs Investigation Team: Shazaad Ahmad, MRCPath (Manchester University NHS Foundation Trust, Oxford Road, Manchester M13 9WL, UK); Felicity Aiano, MSc (Immunisation and Vaccine Preventable Diseases Department, UK Health Security Agency, London, UK); Gayatri Amirthalingam, MFP (Immunisation and Vaccine Preventable Diseases Department, UK Health Security Agency, London, UK); Frances Baawuah, MRCP (Immunisation and Vaccine Preventable Diseases Department, UK Health Security Agency, London, UK); Joanne Beckmann, MRCPCH(UK) (East London NHS Foundation Trust, 9 Allie Street, London E1 8DE, UK); Andrew J Brent, FRCP (Oxford University Hospitals NHS Foundation Trust, Old Road, Oxford OX3 7HE; University of Oxford, Wellington Square, Oxford OX1 2JD, UK); Bernadette Brent, MD (Oxford University Hospitals NHS Foundation Trust, Old Road, Oxford OX3 7HE; University of Oxford, Wellington Square, Oxford OX1 2JD, UK); Kevin E Brown, FRCPath (Immunisation and Vaccine Preventable Diseases Department, UK Health Security Agency, London, UK); Joanna Garstang, MBCHB (Birmingham Community Healthcare NHS Trust, Holt Street, Aston B7 4BN, UK); Ifeanyichukwu O. Okike, PhD FRCPCH (UK) (Derbyshire Children's hospital (University hospitals of Derby and Burton NHS Foundation Trust), Uttoxeter New Road, Derby, DE22 3NE, UK); Mary E Ramsay, FFPH (Immunisation and Vaccine Preventable Diseases Department, UK Health Security Agency, London, UK). This study was funded by the Medical Research Council UK Coronavirus Immunology Consortium (UK-CIC, MR/V028448/1) and the National Core Studies (NCS) programme (MC_PC_20031). The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. Download .docx (.09 MB) Help with docx files Supplementary material.